The present invention relates to a pilot-type two-port vacuum valve connected between a vacuum chamber and a vacuum pump and used for reducing pressure in the vacuum chamber to vacuum pressure.
For example, if gas such as process gas at atmospheric pressure or high pressure in a process chamber is exhausted rapidly in reducing pressure in the chamber to vacuum pressure by a vacuum pump in a manufacturing process of a semiconductor, a large amount of gas flows temporarily. As a result, gas turbulence occurs in the chamber, a cloud of particles deposited on a chamber inner wall or the like is raised, and the particles may be deposited on a workpiece such as a semiconductor wafer.
In order to avoid the above circumstances, there is proposed one in which a tapered valve seat having a tapered face with a width increasing outward and a valve body having a tapered portion are provided to a vacuum valve disposed in a flow path connecting a vacuum chamber and a vacuum pump and a gap between the valve body and the tapered face, i.e., a valve opening degree is gradually changed by moving the valve body along a center line of the tapered valve seat to thereby restrictively exhaust the vacuum chamber. There is also proposed one in which a valve stroke is subtly changed by controlling fluid pressure by an electropneumatic proportional valve to thereby subtly change a valve opening degree.
However, in the vacuum valve having the tapered valve body and the tapered valve seat as described above, because an opening diameter of the valve seat is large, a rise in a gas flow rate for a valve stroke is large and it is substantially difficult to slowly exhaust the vacuum chamber. In a method for subtly changing the valve opening degree by the electropneumatic proportional valve, the electropneumatic proportional valve is required to have extremely high precision and a control mechanism is complicated, and the control lacks stability.
The present invention has been made with the above problems in view and it is an object of the invention to provide a pilot-type two-port vacuum valve in which a flow path can be gradually opened to slowly exhaust a vacuum chamber, a structure and operation of which are simple and easy, and which has excellent operation stability.
The above and other objects and novel features of the invention will become apparent from description of the present specification and the accompanying drawings.
To achieve the above object, according to the invention, there is provided a vacuum valve comprising: a first port to be connected to a vacuum chamber and a second port to be connected to a vacuum pump; a main flow path for connecting the first port and the second port and having a large cross-sectional area and an auxiliary flow path having a smaller cross-sectional area than the main flow path; a main valve body for opening and closing the main flow path and an auxiliary valve body for opening and closing the auxiliary flow path; a first piston connected to the main valve body through a first shaft and a second piston connected to the auxiliary valve body through a second shaft; a main pressure operating chamber for causing fluid pressure in a valve opening direction to act on the first piston and an auxiliary pressure operating chamber for causing fluid pressure in a valve opening direction to act on the second piston; a connecting hole for connecting the main pressure operating chamber and the auxiliary pressure operating chamber to each other; one operating port for supplying pressure fluid to the main pressure operating chamber and the auxiliary pressure operating chamber; and first spring means having large repulsing force for repulsing the main valve body in a closing direction and second spring means having small repulsing force for repulsing the auxiliary valve body in a closing direction.
There are such relationships between piston diameters of the first piston and the second piston and repulsing forces of the first spring means and the second spring means that the second piston is actuated by lower fluid pressure than the first piston.
In the vacuum valve of the invention with the above structure, if fluid of necessary pressure is supplied from the operating port to the main pressure operating chamber and the auxiliary pressure operating chamber, the second piston is first actuated against the repulsing force of the second spring means to open the auxiliary valve body. As a result, the first port and the second port communicate with each other through the auxiliary flow path having the small cross-sectional area and the vacuum chamber is slowly exhausted because of a small rise of a gas flow rate.
Then, if fluid pressure of the operating port increases, the first piston is actuated against the repulsing force of the first spring means to open the main valve body. As a result, the first port and the second port communicate with each other through the main flow path having the large cross-sectional area to thereby facilitate exhausting of the vacuum chamber.
Therefore, according to the vacuum valve of the invention, by only supplying pressure fluid a degree of which is controlled from the one operating port, it is possible to open the main valve body and the auxiliary valve body over time to slowly exhaust the vacuum chamber. Furthermore, the structure and operation are simple and easy and operation stability is excellent.
In the invention, it is preferable that the auxiliary valve body is formed of a needle valve and has a plurality of continuous tapered portions having different inclinations. As a result, it is possible to change the rise of the gas flow rate according to the opening degree of the needle valve.
According to another concrete embodiment of the invention, the vacuum valve has setting means for setting an opening degree of the auxiliary valve body. The opening degree setting means includes a setting rod a position of which can be adjusted to determine an open stroke end of the auxiliary valve body by coming into contact with the second shaft or the second piston and an adjusting member for adjusting the position of the setting rod.
According to another concrete embodiment of the invention, the main valve body is formed to have a larger sealing portion diameter than the auxiliary valve body and the first piston is formed to have the piston diameter larger than that of the second piston. The auxiliary flow path and the auxiliary valve body are incorporated into the main valve body, the second piston and the auxiliary pressure operating chamber are incorporated into the first piston, and the first shaft is inserted into the second shaft.
In this embodiment, if the opening degree setting means for setting the opening degree of the auxiliary valve body is provided, the setting rod is screwed to the first piston and disposed to move with the first piston and also functions as detecting means for detecting an opening degree of the main valve body from a moving amount of the first piston.
Otherwise, it is also possible to provide opening degree detecting means for detecting opening degrees of both the main valve body and the auxiliary valve body. The detecting means has one detecting rod moving in synchronization with both the first piston and second piston to detect the opening degrees of the main valve body and the auxiliary valve body from moving amounts of the first piston and the second piston output by the detecting rod.